1. Field of the Invention
This invention relates generally to formation interval straddle packer tools that are used in casing lined wellbores for formation zone fracturing or other formation treating operations. More particularly, the present invention concerns a straddle packer tool having a valving system which permits bypass of well fluid below the tool to the wellbore above the tool, permits well formation treatment, such as formation fracturing, to be accomplished, and permits bypass of well fluid above the tool to the wellbore below the tool.
2. Description of Related Art
After a wellbore has been drilled, various completion operations are typically performed to enable production of wellbore fluids. Examples of such completion operations include the installation of casing, production tubing, and various packers to define or isolate zones within the wellbore. Also, a perforating string is lowered into the wellbore and fired to create perforations in the surrounding casing lining the wellbore and to extend the perforations into the surrounding formation.
To further enhance the productivity of the formation, fracturing of the formation may be performed. Typically, fracturing fluid is pumped into the wellbore to fracture the formation so that fluid flow conductivity in the formation is improved to provide enhanced fluid flow into the wellbore.
A typical fracturing string includes an assembly carried by tubing, which may be coiled tubing, or jointed tubing such as drill pipe, with the assembly including a straddle packer tool having sealing elements to define a sealed interval into which fracturing fluids may be pumped for communication with the surrounding formation. The fracturing fluid is pumped down the tubing and through one or more ports in the straddle packer tool into the sealed interval.
Straddle packer tools used for fracturing typically incorporate one or more bypass passages to permit fluid communication between zones above and below the tool. Such bypass passages facilitate run-in of the tool by allowing fluid in the wellbore to move upwardly through the tool as it is run into the well. Likewise, such bypass passages also facilitate pulling the tool out of the well, especially from deep treating depths, without experiencing excessive pulling loads.
However, despite the advantages of bypass passages, they also present a major disadvantage in that they permit pressurized wellbore fluids from below the sealed interval to migrate through the straddle packer tool during fracturing. The presence of such pressurized fluids in the wellbore above the straddle packer tool may make it impossible for the operator controlling the fracturing process to identify problems with the process, such as the breakthrough of fracturing fluids through the formation and into the wellbore above the straddle packer tool.
Additionally, as sand and debris above the straddle packer tool can potentially stick the tool in the well, bypass passages may have screens over their inlet openings to prevent sand and wellbore debris from flowing from the lower zones to the upper zones above the straddle packer tool.
Therefore, a method and apparatus is needed for bypassing wellbore fluids through straddle packers during run-in and pull-out while preventing fluid bypass during fracturing and other well treating operations.
The present invention relates to the use of a check valve in a straddle packer tool bypass passage that prevents flow from the lower zone to the upper zone through the bypass passage during fracturing operations. However, free flow is allowed through the check valve from the upper zone to the lower zone when the straddle packer tool is pulled out of the wellbore. This invention thus allows easy pulling from deep treating depths since displaced fluid can flow from the upper zone to the lower zone through the bypass passage and check valve carrying with it any sand and debris which may have accumulated above the tool.
At times, the lower sealing member of the tool is defined by two oppositely directed lower cup packers. In this case, the lower cup packer is oriented with its open end directed downwardly and prevents flow from zones below the tool from carrying sand and debris to the sealed annulus zone or interval between the upper and lower sealing members. When such a packer arrangement is used, a sleeve valve is used to allow fluid to bypass the check valve when running the tool into the well, thus permitting well fluid displaced by the tool to be displaced through the tool to the wellbore above the tool. The sleeve valve is energized for movement to its closed position by lower packer movement responsive to increase of treatment fluid pressure within the sealed annulus zone. Since the treatment fluid passage and the bypass passage of the tool are not in communication, any treatment fluid within the treatment fluid passage is not compromised in any manner whatever by the bypassed well fluid. When interval pressure is applied during fracturing, the cup packers cause the sleeve valve to close and prevent further flow of fluid through the bypass passage of the tool from lower to upper zones. The sleeve valve remains closed when the straddle packer tool is pulled out of the well and the check valve opens to allow downward flow of well fluids through the bypass passage of the tool and into the wellbore below the tool.